OK at 71 Kg (156 lbs) you do not need a whole lot of volume.
The Go 151 is more than adequate volume.
Yes, the GO 151 would be a good board to start out on, but you could go a bit smaller and get one of the Carve boards or a Futura in the 120-140 liter range if you are sure you no longer need the centerboard or a center fin.
As far as having problems with the centerboard on your last sessions, perhaps it would be better to keep the centerboard up all the time and see how much downwind you get pushed.
As soon as you are planing, you can rail the board slightly and come back upwind quite nicely.
Save the centerboard for if you get seriously downwinded and need to sail backupwind more slowly.
If it feels like skiing when you are going into a jibe, that is good, but you need to learn to move your
back foot across the board to nearer the lee side rail and "bank" the board in a manner similar to a snowboard or "edging" you skis.
Since you are a lady, I would suggest spending a bit more money on a high carbon content very lightweight mast. The mast is the single heaviest part of a sailboard rig and if you take care of it , it
will serve you for many, many years and all those years you will appreciate the light weight.
Hope this helps,